Reciprocating slat conveyors powered by linear hydraulic motors became more than a curiosity in about 1974 when it was discovered that sequencing could best be controlled by controlling the release of oil from the motors rather than the delivery of oil to the motors. The next significant discovery was the discovery that drive units could be used as beams and be subjected to an applied side load contrary to the previous wisdom of the art that linear hydraulic drive units should not be side loaded. This discovery led to the development of a reduced size drive assembly, an early example of which is disclosed in U.S. Pat. No. Re. 35,022, granted Aug. 22, 1995, to Raymond K. Foster, and entitled, "Reduced Size Drive/Frame Assembly For A Reciprocating Floor Conveyor."
An effort has been made to use terms herein that will name the drive assembly components without imposing detail or limitations that are not necessary to the invention. A "linear hydraulic motor" is but one of many names given to a hydraulic device that is composed of piston and cylinder components, one of which is fixed and the other of which is allowed to move back and forth along a linear path. Movement is caused by introducing and removing hydraulic fluid pressure to and from variable volume working chambers formed by and between the fixed and movable components. "Linear hydraulic motors" are also termed "linear actuators", "linear hydraulic drive units", and simply "hydraulic cylinders". A problem with calling them "hydraulic cylinders" when it is necessary to describe them in some detail is that one of the components of the device is also referred to as a "cylinder" or "cylinder component." Herein, the "linear hydraulic motors" that will be described are broadly referred to as "linear hydraulic drive units." The piston components of these drive units are composed of piston rods and piston heads. Each cylinder component includes a tubular or cylindrical sidewall, a cylinder head at one end through which the piston rod extends, and an end wall at the opposite end. Herein, the term "cylinder tube" is used to name the cylinder sidewall.
U.S. Pat. No. 4,821,898, granted Apr. 18, 1989 to Raymond K. Foster, and entitled "Drive/Frame Assembly For A Reciprocating Floor" discloses a drive assembly that is similar to the drive assembly disclosed in the aforementioned U.S. Pat. No. Re. 35,022 except that its drive units are a tandem type having fixed opposite end portions that are piston components and a movable central portion that is a cylinder component. This particular type of tandem drive unit eliminates external hoses by incorporating some of the fluid passageways in the piston rods.
U.S. Pat. No. 4,691,819, granted Sep. 8, 1987, to Olof A. Hallstrom, and entitled, "Reciprocating Conveyor", discloses tandem drive units having fixed cylinder components at their ends and a movable central piston component. A problem with this drive unit is that it requires the use of a considerable amount of external hoses. In a commercial embodiment, manufactured by Hallco Mfg. Co., Inc. of Tillamook, Oreg., named the Hallco model 4000 conveyor, the cylinder components are of a tie bolt construction and include a manifold at each end. The inward manifolds include some fluid passageways. However, hoses are used to connect the two manifolds at one end of the drive assembly to the two manifolds at the opposite end of the assembly. This construction of the Hallco model 4000 conveyor is disclosed in a Hallco owner's manual that is published by Hallco Mfg. Co., Inc.
Other prior art drive assemblies utilizing tandem linear hydraulic motors are disclosed in U.S. Pat. No. 5,638,943, granted Jun. 17, 1997 to Raymond K. Foster, and entitled "Drive Assembly For Reciprocating Slat Conveyors." FIG. 4 of this patent discloses a drive assembly that is marketed in Europe by Cargo Handling Systems, B.V., located in Coevorden in the Netherlands. This system utilizes passageways in the piston rods in lieu of some of the hoses but continues to use hoses or conduits for connecting the outward ends of the hydraulic drive units with each other and with a main operating valve, or switching valve, and with a directional control valve. The directional control valve, together with other components of the system, adapts the conveyor for both two way loading and unloading.
All of the prior art drive assemblies that utilize tandem drive units also utilize poppet type sequencing valves that are either built into the cylinder components or provided as an auxiliary structure. The aforementioned U.S. Pat. No. 4,821,863 shows sequencing valves that are auxiliary structure. The-Hallco Model 4000 conveyors have check valves built into its inner manifolds. These check valves are essentially like the check valves disclosed in U.S. Pat. No. Re. 35,022. Cargo Handling Systems, B.V. builds poppet type sequencing valves into the outward ends of the cylinder components.
Richard T. Gist of Tulare, Calif., has developed a drive assembly for reciprocating slat conveyors which uses spool valves for sequencing in place of poppet type check valves. Portions of the piston rods provide the valve spools. However, this drive assembly continues to require the use of external hoses or pipes.
An object of the present invention is to provide an improved drive assembly in which poppet sequencing valves and external hoses are essentially eliminated. The valve that switches the system between loading and unloading modes is incorporated into a housing that is integrated with a cylinder head forming member. The piston rods and piston rod openings in cylinder head forming members together provide the sequencing valves.
Another object of the invention is to provide a conveyor drive that is simple in construction, is durable in use, is efficient in operation, and can be economically manufactured.